The goal of this clinical trial is to investigate the use of pentoxifylline (PTX) as a novel pharmacologic agent for patients with Crohn's disease (CD). CD is a chronic, relapsing inflammatory bowel disease (IBD) that cannot be cured with either surgery or currently available medical therapies. CD is characterized histologically by transmural infiltration of the intestine with T-cells, B-cells, and macrophages, and clinically by abdominal pain, diarrhea, and weight loss. Although the etiology of CD remains elusive, the host systemic and mucosal immune system are central to the disease pathogenesis. The factors responsible for the initiation and perpetuation of the damaging immune responses are unknown, but increasing evidence implicates cytokines, soluble mediators of inflammation, in this process. Pro-inflammatory cytokines, such as tumor necrosis factor alpha (TNF-alpha) and interleukin 1 beta (IL-1beta), are central to the modulation of mucosal inflammation. The central hypothesis of this proposal is that PTX will improve clinical symptoms of patients with CD by selectively decreasing TNF-alpha levels in the intestinal mucosa. This hypothesis will be tested by the following specific aims: Aim 1: Investigate the efficacy and safety of PTX in the treatment of CD. Aim 2: Measure mucosal production of TNF-alpha before and after treatment with pentoxifylline.